• Corpus ID: 15785168

Birth order effects in the formation of long-term relationships

@inproceedings{Hartshorne2009BirthOE,
  title={Birth order effects in the formation of long-term relationships},
  author={Joshua K. Hartshorne and Nancy Salem-Hartshorne and Timothy S Hartshorne},
  year={2009}
}

• Joshua K. Hartshorne, Nancy Salem-Hartshorne, T. Hartshorne
• Published 2009
• Psychology

Researchers have debated for 134 years whether birth order has long-term effects on the development of a child, and so far no consensus has emerged. In addition to practical applications and relevance to the study of personality, birth order effects are an important test case for theories about how and whether home environment affects the adults children become (Pinker, 2002; Sulloway, 1996). In two large surveys of diverse populations, we found that people are more likely to form close platonic and romantic relationships with other people of the same birth order. This effect cannot be explained by confounds of family size. Birth order effects in relationships 3 Birth Order Effects in The Formation of Long-Term Relationships In 1874, Francis Galton noted that first-born sons and only sons were overrepresented among scientists (Galton, 1874), making birth order one of the first constructs studied in psychology. Presciently anticipating the next 134 years of debate, he attributed this effect to both practical circumstances – “they are more likely to become possessed of independent means, and therefore able to follow the pursuits that have most attraction to their tastes.” – and their “independence of character,” a result of having been treated more as companions by their parents (Galton, 1874, pp. 34-35). Since then, numerous studies (Ernst & Angst, 1983; Harris, 1998; Sulloway, 1996) have investigated systematic differences in intelligence, achievement and personality between children of different birth orders. A number of theories have been postulated to account for such differences, generally focusing on the fact that each child’s home environment is at least partly a function of their birth order. In 1918, Alfred Adler gave what is likely the first comprehensive account of birth order, focusing on “dethronement” (Ansbacher & Ansbacher, 1956). The eldest child was, at some point, the center of attention; this is lost with the addition of a sibling. Younger children, in contrast, see their elder siblings as “pacesetters,” and race to catch up. The youngest child, in contrast, is never dethroned. A number of effects on personality are predicted on this basis. Sulloway (1996), in contrast, explains birth order effects in terms of children diversifying in order to better compete for scarce resources, such as parental investment. This leads, under his account, to the eldest child identifying with her Birth order effects in relationships 4 parents and the establishment in general, while younger children are more open to new experiences and are generally more rebellious. Other accounts exist as well. Not only has no single birth order theory been established, but even the existence of birth order effects remains highly controversial (Bjerkedal, Kristensen, Skjeret, & Brevik, 2007; Harris, 2006; Sulloway, 2007; Wichman, Rodgers, & MacCallum, 2007). This is at least in part because of methodological problems. Poor families tend to have more children, and thus any cross-sectional study confounds birth order with socio-economic status (SES). A correlation between being a later-born child and being more rebellious may in fact just be a correlation between SES and rebelliousness (Ernst & Angst, 1983; Harris, 1998; Sulloway, 1996; Wichman, Rodgers, & MacCallum, 2006). However, even among studies that control for such between-family factors, there has been little agreement (Ernst & Angst, 1983; Harris, 1998; Sulloway, 1996; Wichman, Rodgers, & MacCallum, 2006). The debate over birth order effects has important implications for a number of fields. Adlerian theorists and clinical practitioners make frequent use of birth order theory (Eckstein, 2000; Laird & Shelton, 2006; Marshall & Fitch, 2006; Tobin & McCurdy, 2006). For this group, the ongoing empirical uncertainty about the existence of birth order effects can be unsettling (Manaster, 1977). The existence of birth order effects is interesting in its own right and may have practical applications. Birth order effects have also become an important test case in the Nature versus Nurture debates. Harris (1998; 2006) and Pinker (2002) both argue that the literature has conclusively shown that birth order does not affect personality outside of the home, and they use this to help build their case that a child’s home Birth order effects in relationships 5 environment has little to no effect on the adult she becomes. Conversely, the existence of birth order effects on personality or intelligence would be strong evidence that the home environment does help shape the child. In this article, we test for birth order effects in a theory-neutral manner, using a long-term, stable behavior as our dependent measure (the formation of close relationships) rather than personality assessments. Personality assessments are typically based on self-report, the validity of which can be cause for concern, but more importantly are based on an individual’s memories about typical behavior. Decades of memory research show that memory exhibits biases in systematic ways (Schacter, 2001). Moreover, the efficacy of personality assessments even under the best of circumstances has been challenged (Gladwell, 2006). Although previous studies using real-world behavior as a dependent measure have been plagued with the same inconsistencies and methodological problems as the birth order literature as a whole, we believe behavior is more likely to give a stable result. In fact, there is at least one such behavior that appears to be uncontroversially liked to birth order: younger siblings engage in risky behavior earlier (Argys, Rees, Averett, & Witoonchart, 2006; Harris, 2006). However, this may have less to do with personality differences resulting from birth order, and more to do with older siblings exposing younger siblings to such behaviors earlier. In this investigation, we focus on a stable, long-term and ecologically valid behavior: the formation of close platonic and romantic relationships. We assume that if birth order systematically affects personality, and personality systematically affects the Birth order effects in relationships 6 formation of friendship and mating bonds, there should be a relationship between the birth orders of friends and between the birth orders of spouses. Note that this should be true regardless of which positive theory of birth order effects is correct. Birth order studies typically consider one particular trait predicted by a theory to differ across birth orders, such as educational achievement, aggression, self-esteem or conservatism (Ernst & Angst, 1983). Thus, a significant birth order effect can only be found if the birth orders differ on that particular construct (and if it is measured in a well-designed study). In contrast, our method casts a wider net. A small number of studies have investigated birth order effects on mating patterns. The majority of these focused on testing Walter Toman’s “duplication theorem,” which suggested that adults try to recreate in marriage the social dynamics of their childhood (Toman, 1971). Thus, men with only older sisters should be expected to marry women with only younger brothers, and such marriages should be more stable and successful than other birth order combinations. Toman and colleagues reported several studies confirming these hypotheses (Toman, 1971), but these studies were severely criticized on methodological grounds (Birtchnell & Mayhew, 1977). The bulk of subsequent studies failed to support the duplication theorem (Birtchnell & Mayhew, 1977; Gold & Dobson, 1988; Ickes & Turner, 1983; Kemper, 1966; Levinger & Sonnheim, 1965; Mendelsohn, Gruen, & Curran, 1974; Weller, Natan, & Hazi, 1974). Unfortunately, these studies for the most part only tested birth-order combinations relevant to the duplication theorem, thus missing any other potential effects. Birth order effects in relationships 7 Given that spouses appear to correlate on just about every imaginable trait (Burgess & Wallin, 1943; Diamond, 2002; Schiller, 1932), if birth order has any systematic effect on a person that generalized outside of the home environment, the most likely outcome – in contrast with Toman’s theory – is a correlation between the birth orders of spouses. In fact, Burgess and Wallin (1943), in a large study of 1,000 engaged couples, found 14% more oldest-oldest, middle-middle, youngest-youngest and only-only pairings than would be expected by chance. However, this study did not control for SES or total number of siblings (sibship size). As will be discussed below, the same pattern would be expected if children from large, poor families tended to marry each other while children from small, wealthy families married one another. This finding was replicated in one subsequent, smaller study of 146 college faculty which did control for SES, though not for number of siblings (Ward, Castro, & Wilcox, 1974). However, this study dichotomized birth order into first-born and only children versus later-born children, which may not have sufficient sensitivity. This contrasts with a study of 200 pedestrians, which similarly dichotomized birth order but did not control for SES or family size, and found no significant relationship between the birth orders of spouses (Touhey, 1971). Simple power calculations suggest that a 14% effect on this dichotomous data would require 200 participants (100 first-born or only children, 100 later-born children) to achieve a power of .80 (that is, any given experiment with 200 couples and an α = .05 would have an 80% chance of rejecting the null hypothesis which stated no difference) and 331 couples to achieve a power of .95. Thus, at the sample sizes used in the smaller studies, conflicting findings are not unexpected. Birth order effects in relationships 8 Finally, it is worth noting a very early study of 46 first-generation Ashkenazi Jewish couples (thus tightly controlled for SES and ethnicity, if not family size) did not find a st